The invention relates to a carbon brush spring system comprising a carbon brush that is arranged for at a first terminal surface thereof conductively contacting a rotatable collector body for electric current transfer, and furthermore comprising spring means being arranged to at a region of said carbon brush away from said first terminal surface engage with said carbon brush for therewith establishing a current conductive interconnection to an external electric facility, said system furthermore comprising mechanical stabilizing means being arranged for maintaining a stable position of said carbon brush with respect to said rotatable collector body in both radial and tangential directions in a housing. Such carbon brush systems are being used for sliding current transmitters arranged for transmitting electric current to/from commutators in direct current DC motors. A known system has been described in German Patent DE 696 04 440 T2 that has been translated from European Patent EP 741 438 B1 and corresponds to U.S. Pat. No. 5,621,262.
Such system, colloquially called in the art a xe2x80x9cstandard systemxe2x80x9d comprises many parts, such as a guiding member for the carbon brush, a carbon brush spring arrangement that is often executed in the form of a wire formed as a screw, the carbon brush proper which is in particular provided with a loose and flexible contacting conductor, and the contact rail for ultimate connection to a current supply facility. The inventors have recognized that the known arrangement contains too many parts, of which the contacting conductor (the spring) is furthermore quite difficult to maintain operational for extended periods. In fact, various and frequent defects have been reported as occurring.
Another known system is the so-called xe2x80x9chammer carbon brush systemxe2x80x9d, such as used in certain DC motor types of Mabuchi and/or Johnson. Here, the carbon brush and the spring have been permanently connected to each other. However, this set-up is weak in a radial direction. Reversal of the sense of rotation of the motor may cause a tangential dislocation or shift of the carbon brush. Furthermore, if an appreciable amount of wear would inevitably occur, the single-sided support can cause a further tangential shifting of the contact surface, which will have a detrimental effect on the timing characteristics of the motor. Apparently, both known solutions have a negative operational outlook, in particular when operated on a longer time scale.
Now, the present inventors have recognized the particularly advantageous properties of a structure that is substantially symmetric in the tangential direction of the rotation, and which furthermore would have only a low number of parts which parts were structurally and permanently fixated to each other.
In consequence, amongst other things, it is an object of the present invention to present a carbon brush spring system having a substantially symmetric structure in the tangential direction of the rotation that furthermore would have only a spring part and a carbon brush part that were structurally fixated to each other, as according to one of its aspects being characterized by said spring means being constituted by a single body spring part having a substantially symmetric structure in the tangential direction of rotation, being provided with a first section and a second section that collectively constitute said spring part, and a carbon brush part that is structurally fixed to the spring part, said first and second sections constituting a symmetric arrangement between said carbon brush part and respective attachment facilities for fixed connection to said housing, wherein said first and second sections at an intermediate range between said carbon brush and said housing are disposed away from each other at a distance that is appreciably larger than either at said carbon brush or at said housing.
In the above, the symmetric character would apply in particular to the part of the spring that provides the positioning of the carbon brush proper. Further extensions of the spring that would care for other aspects, such as the fixating of the spring itself to the surrounding structure or housing and the connection to the current rail could by themselves be asymmetric with regard to the overall structure of the system. According to these various aspects preferred embodiments of the invention are being characterised as follows.
A preferred embodiment of a carbon brush system according to the invention is characterized in that each said spring part section has a strip-wise cross-section.
A further preferred embodiment of such carbon brush system is characterized in that each said section has at least two bends and is, abstracted from its own strip width, fully disposed in a plane that is substantially perpendicular to the axis of said rotation.
According to another aspect of the invention said carbon brush system is characterized in that each said section forms a major bend between said carbon brush and said housing.
An alternative, preferred embodiment of a carbon brush system according to the invention is characterized in that said fixed connection is formed through bending each said first and second section at least partially around two poles according to at least two minor bends per said first or second section, wherein said poles are fixed to said housing.
Another preferred embodiment of a carbon brush system according to the invention is characterized in that a single section of said first and second sections has an extending part for connecting to a current connector disposed at said housing.
A preferred embodiment of a carbon brush system according to the invention is characterized in that said first and second sections together have the approximate shape of a diamond figure with rounded ends of the tangential axis, being furthermore interconnected at one end of its radial axis end and separated at the other end of its radial axis.
Said tangential axis may be chosen longer than said radial axis.
A preferred embodiment of a carbon brush system according to the invention is characterized in that carbon brush system is provided by one or more axially oriented poles as immediate stoppers against a tangential displacement of said carbon brush.
Said axially oriented poles may be are located substantially adjacent said rotatable collector body.
The invention also relates to a spring part for use in a carbon brush spring system according to the invention, and to a DC motor provided with a system according to the invention. Further advantageous aspects of the invention are recited herein.